Unified Microwave Moisture Sensing Technique for Grain and Seed

Authors: Trabelsi, Samir; Nelson, Stuart

Submitted to: Measurement Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2007
Publication Date: 6/5/2007
Citation: Trabelsi, S., Nelson, S.O. 2007. Unified Microwave Moisture Sensing Technique for Grain and Seed. Measurement Science and Technology.

Interpretive Summary: Moisture content of cereal grains and many other agricultural products is the most important characteristic that determines their suitability for storage, and it is also important in determining the selling price. Electronic moisture meters are used almost universally in the grain trade for determining the moisture content of samples taken from lots being delivered to grain elevators, transportation facilities, processors, etc. However, reliable moisture sensing equipment for continuously monitoring grain and seed moisture content on harvesting equipment, when loading and unloading grain, and in processing is needed to provide better moisture content information for managing these operations. It has been shown that microwave measurements on grain and seed can provide reliable moisture information independent of packing variations that take place while grain is moving in a chute or conveyor. New research has revealed that a single calibration based on the dielectric properties of grain measured at microwave frequencies can reliably sense the moisture content of wheat, corn, grain sorghum, soybeans, and barley. Because these five commodities have very different kernel shapes, sizes, and composition, this new technique offers promise for a universal calibration for grain, soybeans, and similar crops. The new technique provides an incentive for the development of practical microwave moisture sensing instruments that can provide new tools for the maintenance of high quality in such agricultural products, thus benefiting farmers and consumers as well.

Technical Abstract: A unified method for moisture sensing in grain and seed from a single calibration equation, which is obtained from measurement of their dielectric properties at a single microwave frequency is presented. The method is based on a complex permittivity calibration function that is independent of both bulk density changes and the kind of material. Performance of the method was tested for soybeans, corn, wheat, sorghum and barley at 7 GHz and about 23 degrees C. The standard error of calibration for moisture prediction from complex permittivity was 0.8%.